linux-kernel - Re: [PATCH] riscv: fixup max_low_pfn with PFN

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Date:   Wed, 16 Jan 2019 09:07:38 +0800
From:   Guo Ren <guoren@...nel.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     palmer@...ive.com, aou@...s.berkeley.edu,
        linux-arch@...r.kernel.org, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org, Guo Ren <ren_guo@...ky.com>,
        Mao Han <mao_han@...ky.com>
Subject: Re: [PATCH] riscv: fixup max_low_pfn with PFN_DOWN.

Hi Christoph,

I use PFN_DOWN() every where as possible and seems it's a habit
problem. So let risc-v maintainer to choose "PFN_DOW()" or
">> PAGE_SHIFT".

Also the same with "end_of_DRAM & max_low_pfn".

Best Regards
 Guo Ren

On Tue, Jan 15, 2019 at 08:12:54AM -0800, Christoph Hellwig wrote:
> On Wed, Jan 16, 2019 at 12:10:00AM +0800, Guo Ren wrote:
> > > >  	set_max_mapnr(PFN_DOWN(mem_size));
> > > > -	max_low_pfn = memblock_end_of_DRAM();
> > > > +	max_low_pfn = PFN_DOWN(memblock_end_of_DRAM());
> > > 
> > > I know it is used just above, but can we please just switch this
> > > code to use >> PAGE_SHIFT instead of PFN_DOWN, which just horribly
> > > obsfucates what is going on?
> > ???
> > #define PFN_DOWN(x)	((x) >> PAGE_SHIFT)
> > 
> > phys_addr_t __init_memblock memblock_end_of_DRAM(void)
> > {
> > 	int idx = memblock.memory.cnt - 1;
> > 
> > 	return (memblock.memory.regions[idx].base + memblock.memory.regions[idx].size);
> > }
> > 
> > What's the problem? PFN_DOWN() couldn't be used with function call?
> 
> PFN_DOWN gives you the correct result.  But I think it actually
> drastically reduces readability over just opencoding it.
> 
> > My patch just want to point out that max_low_pfn is PFN not size. In fact
> > there is no error for running without my patch :P
> 
> No, I think your patch is correct.  I just wonder if we could make
> the code easier to read.